public static ArrayList DedupStringList(ArrayList list)
        {
            if (list == null)
          {
                return new ArrayList(0);
            }

            ArrayList result = new ArrayList();
            Dictionary<string, string> hashset = new Dictionary<string, string>();
            foreach (string str in list)
           {
                if (string.IsNullOrEmpty(str.Trim()))
               {
                    continue;
                }

                string s = str.Trim().ToLower();

                if (!hashset.ContainsKey(s))
                {
                    hashset.Add(s, string.Empty);
                    result.Add(s);
                }
            }

            result.TrimToSize();
            return result;
        }

------解决方案--------------------
Contains 就只这样
    ArrayList result = new ArrayList() { 1, 2, 3, 3 };
           ArrayList result2 = new ArrayList();
           foreach (var r in result)
           {
               if (!result2.Contains(r)) result2.Add(r);
           }


------解决方案--------------------
 ArrayList result1 = new ArrayList() { 1, 2, 3, 4, 5, 6 };
           ArrayList result2 = new ArrayList() { 5, 6, 7, 8, 9, 10 };
           result1.AddRange(result2);
           var source = result1.Cast<int>().Distinct().ToArray();


------解决方案--------------------
C# code

 public static void Main(string[] args) { 
                 int[] A = { 1, 2, 2, 4, 5, 3 };
                 int[] B = { 2, 4, 5, 7, 5, 6, 8 }; 
             //1.1， 合并以上两个数组，合并结果不包含重复项，并排序。
            //要求结果为: 1,2,3,4,5,6,7,8
               A.Concat(B).Distinct().OrderBy(i => i).ToList().ForEach(i => Console.Write(i.ToString()));
             Console.WriteLine(Environment.NewLine);
            //2，去除以上两个数组中所有重复项，并合并，并排序。
            //要求结果为: 1,3,6,7,8
 A.Except(B).Concat(B.Except(A)).OrderBy(i => i).ToList().ForEach(i => Console.Write(i.ToString()));
}